1. Field of the Invention
The present invention relates to a method and system for controlling an output in an X-ray apparatus.
2. Description of the Related Art
In an X-ray diagnosis apparatus, in order to radiate an X-ray to an object to be examined, a voltage generating apparatus is used to apply a tube voltage to an X-ray tube. This voltage generating apparatus includes an AC-DC converter for converting an AC voltage into a DC voltage.
As shown in FIG. 1, the AC-DC converter includes an AC power source 1, a rectifying circuit 2, a smoothing capacitor C, and a load resistor RL.
In the rectifying circuit 2, series-connected diodes D1 and D2 are connected in parallel to series-connected diodes D3 and D4. An AC voltage from the AC power source 1 is applied to terminals a and b of the rectifying circuit 2 through a power source resistor re, and the applied voltages are full-wave rectified. Thereafter, the rectified voltages are output through terminals c and d, respectively. An output voltage from the rectifying circuit 2 is smoothed by the capacitor C. A voltage of the capacitor C is applied to the load resistor RL.
Since the capacitor C is directly connected to the rectifying circuit 2, an impedance of the AC-DC converter is nonlinear with respect to a power source voltage of the AC power source 1, and a harmonic current flows into the AC power source 1.
As shown in FIG. 2, since a current i includes an odd-numbered order harmonic component with respect to a power source voltage V of the AC power source 1, the power source voltage V is distorted. If the content of harmonic component is large, a power factor is reduced. Therefore, in order to supply constant power to the load resistor RL, a large-capacitance AC power source must be used.
Power is supplied from the capacitor C to the load resistor RL during an X-ray radiation period. A power E can be obtained as: EQU E=C.multidot.(.sqroot.2e).sup.2 .multidot.[1-{RL/(RL=re)}.sup.2 ]/2
Therefore, power supplied from the capacitor C to the load resistor RL is determined in accordance with an impedance value of the load resistor RL and the power source resistor re. For example, when RL/(RL+re).gtoreq.0.9, only about 20% of the total capacitance of the capacitor C can be supplied.
As described above, an X-ray generating apparatus which can improve a power factor by reducing a harmonic component of current, and can efficiently supply power from a capacitor to an X-ray tube is desirable.